subcutis – the bottom layer of skin that consists of a layer of fat and collagen (a tough, spongy protein), which helps protect the body and regulate temperature

Causes of cellulitis

Cellulitis develops when bacteria, or sometimes fungi, move down through the skin’s surface into the dermis and subcutis through a damaged or broken area of skin, such as a cut, burn or bite.

Having a skin condition such as eczema or a fungal infection of the foot or toenails (athlete’s foot) can cause small breaks and cracks to develop in the surface of the skin. This makes a person more vulnerable to cellulitis.

Other known risk factors for cellulitis include:

having a weakened immune system (the body’s natural defence against infection and illness) as a result of health conditions such as HIV or diabetes, or as a side effect of a treatment such as chemotherapy

lymphoedema – a condition that causes swelling of the arms and legs, which can sometimes occur spontaneously or may develop after surgery for some types of cancer

Symptoms of cellulitis

See your doctor immediately if an area of skin suddenly turns red, hot and tender. If you cannot see your doctor on the same day, you should go to an emergency medical centre such as accident and emergency.

Certain symptoms can indicate that the infection has spread from your skin to other parts of the body, such as the blood. These include vomiting, fever, rapid breathing and confusion or disorientation. If you experience these symptoms, call for an ambulance.

In some cases of cellulitis the bacteria triggers a secondary infection somewhere else in the body, such as in the blood (septicaemia). Such cases usually require hospital admission for treatment with intravenous antibiotics (antibiotics given directly into a vein).

Glossary

Antibiotics are medicines that can be used to treat infections caused by microorganisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin.

Bacteria are tiny, single-celled organisms that live in the body. Some can cause illness and disease and some others are good for you.

Inflammation is the body's response to infection, irritation or injury, which causes redness, swelling, pain and sometimes a feeling of heat in the affected area.

Symptoms

Cellulitis causes the area of affected skin to become red, hot, swollen, and tender or painful.

Cellulitis most commonly affects one of your legs, although symptoms can develop in any area of your body.

If you have cellulitis, you may also find that blisters develop on your skin.

Cellulitis can make you feel generally unwell, causing symptoms that develop before, or in combination with, changes to your skin. These symptoms include:

nausea

shivering

chills

a general sense of feeling unwell

When to seek medical advice

See your doctor as soon as possible if an area of your skin suddenly turns red, painful and hot.

If it is not possible for you to see your doctor on the day your symptoms develop, you should visit your local minor injuries unit.

When to seek urgent medical advice

Additional symptoms can suggest that the infection has begun to spread from your skin to other parts of your body, such as your blood.

If you have any of these symptoms, go to your nearest accident and emergency (A&E) department as soon as possible, because you may need urgent medical attention.

These symptoms include:

rapid spreading of the area of redness

high temperature (fever) of 38ºC (100.4ºF) or above

vomiting

changes in mental state, such as confusion

rapid heart beat

rapid breathing

dizziness, particularly when moving from a lying or sitting position to a standing one

Fever A high temperature, also known as a fever, is when someone's body temperature goes above the normal 37°C (98.6°F).

Causes

Most cases of cellulitis are caused by an infection of the tissues beneath the skin with either the group A streptococcus or staphlococcus aureus bacteria.

See streptococcal infections and staphyloccocal infections for more information about these types of bacteria.

Cellulitis usually occurs when the surface of your skin is damaged. This damage creates an entry point for the bacteria, allowing them to attack the skin and tissue underneath. A break in the skin may be caused by a:

The break in the skin may be so small that it cannot be easily identified.

Some cases of cellulitis can develop if a wound or other break in the skin is exposed to water that is contaminated with bacteria.

A fungal infection is a much rarer cause of cellulitis. Fungal cellulitis usually only affects people with a severely weakened immune system, such as a person in the final stages of an HIV infection that is not responding to treatment.

Who is at risk?

A number of health conditions can increase your risk of developing cellulitis. These include:

being obese (excessively overweight)

having a weakened immune system

having poorly controlled diabetes

having circulation problems

having chickenpox or shingles

having lymphoedema

having long-term untreated athlete's foot or fungal toenail infection

intravenous drug use

having previous episodes of cellulitis

These are briefly discussed below.

Obesity

Being obese can cause swelling in your legs, which may increase your risk of developing cellulitis.

Obesity is defined as being very overweight with a body mass index (BMI) of 30 or more.

Weakened immune system

Your immune system may be weakened if you have a condition such as HIV and AIDS. Having a weakened immune system makes it harder for your body to fight off infection.

A number of treatments are also known to weaken the immune system. For example:

Circulation problems

Poor circulation can increase your risk of developing skin infections in the places where your body does not have an adequate blood supply.

For example, many people with diabetes have a reduced blood supply to their feet, which makes them more vulnerable to developing cellulitis.

Chickenpox and shingles

Chickenpox and shingles often cause blisters to develop on your skin. Chickenpox (which usually only affects children) and shingles (which usually affects people aged 50 and older) are viral infections caused by the herpes varicella-zoster virus.

If the blisters that occur in chickenpox or shingles are broken or scratched, it can damage your skin and provide an entry point for bacteria.

Lymphoedema

Lymphoedema is a condition that causes fluid to build up under your skin. It may occur following surgery for some cancers. If your skin becomes very swollen it may crack, creating an entry point for bacteria.

Intravenous drug use

People who inject illegal drugs have an increased risk of developing cellulitis, because poor needle hygiene, such as not sterilising the needle before and after injections, can increase the risk of infection.

Previous episodes of cellulitis

If you have had a previous episode of cellulitis, your risk of having episodes in the future increases.

An estimated 20-30% of people with a previous history of cellulitis will be admitted to hospital again with another cellulitis infection. The average time between a previous and recurring cellulitis infection is three years.

Glossary

Chronic Chronic usually means a condition that continues for a long time or keeps coming back. Immune system The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses. Liver The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy. Obesity Obesity is when a person has an abnormally high amount of body fat. Veins Veins are blood vessels that carry blood from the rest of the body back to the heart.

Diagnosis

Before making a diagnosis, your doctor may want to rule out other conditions that can lead to your skin becoming red and inflamed, such as varicose eczema (an itchy skin condition that causes inflammation and, sometimes, skin ulcers).

If you have an open wound in your skin, your doctor may take a swab of cells from the wound to see what type of bacteria is causing the infection. A swab looks similar to a cotton bud and it is used to remove small traces of tissue for testing.

Further testing may be carried out if your symptoms are serious enough to warrant admission to hospital. Testing usually involves a series of blood tests, which are an effective way of assessing the severity of the infection and how well you are responding to the antibiotics. See treatment of cellulitis for more information.

Treatment

If you are diagnosed with cellulitis, your treatment will depend on the cause of your cellulitis, the severity of your symptoms, and the general state of your health.

You can usually be treated at home with antibiotic tablets if you do not have additional symptoms of being unwell, such as fever, nausea and vomiting, that suggest the cellulitis infection has spread from your skin to the bloodstream or other parts of the body.

If this is not the case admission to hospital is usually recommended.

Treatment at home

Antibiotics

If you are well enough to be treated at home, you will be given a seven-day course of antibiotic tablets.

The most commonly prescribed antibiotic for cellulitis is flucloxacillin, which is part of the penicillin group of antibiotics.

The most common side effects of flucloxacillin are mild digestive problems, such as an upset stomach or episodes of diarrhoea.

If you cannot take flucloxacillin because you are allergic to penicillin, an alternative antibiotic known as erythromycin can be used.

The side effects of erythromycin are usually mild and short-lived. They include nausea, abdominal (tummy) discomfort, vomiting and diarrhoea

If it is suspected that your cellulitis was caused by a wound being exposed to contaminated water, you will be given a combination of two different antibiotics: usually doxycycline or ciprofloxacin in combination with flucloxacillin or erythromycin.

When you first start taking the antibiotics, you may notice that your skin becomes redder. This is usually only a temporary reaction, and the redness should start to fade within 48 hours.

Contact your doctor immediately if your symptoms get worse 48 hours after taking the antibiotics, or you develop additional symptoms, such as a high temperature or vomiting.

Self-care

There are steps you can take at home to ease your symptoms and speed your recovery from cellulitis.

Drink plenty of water to prevent dehydration. If your leg is affected by cellulitis, keep it raised. This should make you feel more comfortable and help to reduce the swelling.

Pain relief

If your cellulitis is causing pain or a high temperature (fever), an over-the-counter painkiller may ease your symptoms. Paracetamol and ibuprofen are suitable for cellulitis.

Treatment at hospital

If you need to be admitted to hospital for treatment, you will be given antibiotics directly into your vein through an injection or a drip (known as intravenous antibiotics).

The type of antibiotics that will be used depends on the suspected cause of your infection, although a type of antibiotic known as a broad-spectrum antibiotic is often used. This type of antibiotic can kill a range of different strains of bacteria.

If your symptoms improve and you are otherwise healthy, you may be discharged after 48 hours and your treatment can switch to antibiotic tablets.

If this is not the case, a three or four day course of intravenous antibiotics is usually recommended before switching over to antibiotic tablets.

Glossary

Antibiotics Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin. Fever A high temperature, also known as a fever, is when someone's body temperature goes above the normal 37°C (98.6°F). Kidney Kidneys are a pair of bean-shaped organs located at the back of the abdomen, which remove waste and extra fluid from the blood and pass them out of the body as urine. Liver The liver is the largest organ in the body. Its main jobs are to secrete bile (to help digestion), detoxify the blood and change food into energy.

Complications

Complications of cellulitis can include blood poisoning, abscesses, and meningitis.

Blood poisoning

If the bacteria that infect your skin and tissue enter your bloodstream, they can cause blood poisoning (septicaemia). Symptoms of blood poisoning include:

Abscess

Some cases of cellulitis can result in an abscess forming near the site of the infection.

An abscess is a swollen, pus-filled lump under the surface of the skin. It is caused by a build-up of bacteria and dead white blood cells.

In some cases, the antibiotics that are used to treat cellulitis may also help to remove the abscess. However, if this is not the case, the pus will have to be drained from the abscess through a small cut in your skin.

Facial cellulitis and meningitis

Facial cellulitis is an uncommon form of cellulitis that develops on the skin of the face. It accounts for an estimated 8.5% of all cases of cellulitis.

Facial cellulitis is most common in children under three years old and older adults above 50. If facial cellulitis is left untreated in children, the bacteria can potentially spread to the outer membranes of their brain (the meninges) and trigger a serious brain infection called meningitis.

Symptoms of meningitis can differ in adults, but symptoms in babies and children under three years old include:

becoming floppy and unresponsive, or stiff with jerky movements

becoming irritable and not wanting to be held

unusual crying

vomiting and refusing feeds

pale and blotchy skin

loss of appetite

staring expression

very sleepy and reluctant to wake up

Bacterial meningitis is very serious and should be treated as a medical emergency. If left untreated, a bacterial infection can cause severe brain damage and infect the blood.

If you suspect that your child has symptoms of meningitis, call immediately for an ambulance.

The best way to protect your child against meningitis is to make sure they have been vaccinated with the:

DTaP/IPV/Hib (5-in-1) vaccination, which should be given between the ages of two and four months

the Hib/MenC booster, which should be given after the child’s first birthday

The vaccine and the booster provide immunity against two leading causes of meningitis in children:

haemophilus influenzae type b bacteria

group C meningococcal bacteria

Ask your doctor if you are unsure whether your child’s vaccinations are up to date.

Glossary

Abscess An abscess is a lump containing pus, which is made by the body during infection. Antibiotics Antibiotics are medicines that can be used to treat infections caused by micro-organisms, usually bacteria or fungi. For example amoxicillin, streptomycin and erythromycin. Heart valves Heart valves are four sets of flaps that control the direction that blood pumps around the heart. Vein Veins are blood vessels that carry blood from the rest of the body back to the heart.

Prevention

Not all cases of cellulitis can be prevented. But you can take steps to reduce the risk of developing the condition.

These involve steps to prevent skin wounds, and treating wounds properly when they occur.

Treating skin wounds

Make sure that any cuts, grazes or bites are kept clean. Wash the damaged skin under running tap water and, if necessary, apply an antiseptic cream.

Keep the wound covered with a plaster or dressing. Make sure you change the plaster or dressing if it becomes wet or dirty. Plasters and dressings will reduce the risk of the wound being damaged further, and they will help to create a barrier against bacteria entering the skin.

Hand hygiene

If you have an itchy skin condition, such as atopic eczema or chickenpox, keep your fingernails clean and short at all times.

If you scratch your skin and your fingernails are short and clean, the risk of skin damage and infection will be reduced.

Keep your skin moisturised

If your skin is dry or prone to cracking, keep your skin well moisturised. Cracked skin can create an entry point for bacteria.

Preventing cellulitis in lymphoedema

People with lymphoedema (a condition that causes swelling of the arms and legs) have a much higher risk of developing cellulitis than others. This is because the swelling of the skin that is associated with lymphoedema makes it more vulnerable to bacterial infection.

If you are diagnosed with lymphoedema, you may be given a two-week course of antibiotics to take in case you start having the initial symptoms of cellulitis.

If you have two or more episodes of cellulitis in a year, it is usually recommended that you begin taking antibiotics on a long-term basis to protect against further infection.